1. Field of the Invention
This invention relates to a navigation system and method for providing lane guidance by the use of fork schematic drawings made in accordance with data on a fork pattern, and relates to a storage medium therefor.
2. Description of the Related Art
In a conventional navigation system, lane guidance has been provided for, at a predetermined distance before a fork when a vehicle is running on an expressway or the like, giving the driver a guidance on which lane to take, by displaying arrows on fork schematic drawings. The fork schematic drawings prepared as lane-guiding data in a database have been hitherto determined by manual labor based on a field survey.
In addition, a lane-guiding method has been proposed in which a storage medium that stores guiding data is accessed when running, and data on the number of lanes at a predetermined distance before a fork and data on the number of lanes immediately before the fork are extracted, so that a fork schematic drawing is calculated and displayed for lane guidance.
However, the manner of manual labor based on the field survey entails high cost and much time, and therefore is extremely inefficient for collecting data. Also, because the data are collected by manual labor, the data quality easily varies depending on the surveyor.
On the other hand, with the method in which the fork schematic drawing is calculated when running, the calculation cannot be finished in time in, for example, Germany where the average velocity of vehicles is extremely high, so that a case occurs in which lane-guiding information cannot be provided opportunely to the driver.
It is therefore an object of the present invention to digitize lane-guiding information efficiently. Additionally, it is another object of the present invention to opportunely provide lane-guiding information even when running at a high speed.
According to a first aspect of the invention, a navigation system comprises information storage means for storing map data including fork pattern data, retrieval means for acquiring fork information from the map data and retrieving a connection between an entrance lane and an exit lane and a number of lanes at an acquired fork, and fork schematic drawing generation means for generating a schematic drawing of a corresponding fork by selecting fork pattern data based on the connection between an entrance lane and an exit lane and the number of lanes that have been retrieved.
According to a second aspect of the invention, the fork schematic drawing generation means judges whether or not there is a merging point within a predetermined distance before the fork and, if there is a merging point, it is added to the fork schematic drawing.
According to a third aspect of the invention, the fork schematic drawing generation means judges whether or not there is another fork within a predetermined distance after the fork and, if there is another fork, a successive fork schematic drawing is generated by adding it to the fork schematic drawing.
According to a fourth aspect of the invention, a navigation system for route-guidance on a road whose name differs depending on the district comprises district judging means for judging which district a fork belongs to, and guide means for guiding a driver using the name of the road in accordance with the district to which the fork belongs based on the result of judgement by district judging means.
According to a fifth aspect of the present invention, a method for displaying navigation data comprises the steps of acquiring fork information from map data, retrieving a connection between an entrance lane and an exit lane and the number of lanes at an acquired fork, and generating a schematic drawing of a corresponding fork by selecting fork pattern data based on the connection between an entrance lane and an exit lane and the number of lanes that have been retrieved.